Import the individual tiles or tilesheet images for your Isometric Tilemap into your Unity Project by placing the textures into the Assets folder. Select the imported images to view their Texture Importer settings in the Inspector window.
When importing Sprites for use in an Isometric Tilemap, use the following recommended settings. For further information about each setting, refer to the documentation on Texture Type: Sprite (2D and UI).
In the example below, the imported Sprite is a 256x128 image, and the Isometric Tilemap has a Cell Size of (XYZ: 1, 0.5, 1) Unity units. To make the Sprite fit exactly on a single Cell of the Tilemap, set its PPU value to 256. Its entire width then corresponds to one Unity unit, which is equal to the width (X value: 1) of a single Cell.
If the Sprite is set to a PPU value of 128, then it becomes 2 (256px/128) Unity units in width. This causes the Sprite to visually appear to cover 2 Cells in width when painted on the Tilemap. However, the Tile the Sprite is rendered on remains as a single Cell position.
After the Sprites are imported, refine the outlines of the Sprites by opening the Sprite Editor for each of them and editing their outlines. For Sprites in an Isometric Tilemap, you should set the Pivot of the Sprite so that the ‘ground’ is relative to the Sprite.
If the Texture is imported with Sprite Mode set to Multiple and contains multiple Sprites, then edit the outline of each Sprite in the Sprite Editor.